<?php
declare(strict_types=1); //开启严格模式
function f($x,$y,){
    return 5*$x+3*$y;
}
function f2(int|float $x, int|float $y,): int|float|false{
    if($x>9||$y>9)return false;
    return $x+$y;
}
echo 'f(3,6)=', f(3,6),"\n";
echo 'f(3,6)=', f(1.2,2),"\n";
echo 'f2(3,6)=', f2(3,6),"\n";
echo 'f2(3.8, 6.6)=', @f2(3.8,6.6),"\n";
var_dump(f2(13,10));